The invention disclosed herein pertains generally to material feeders and more particularly to a feeder for fluid-like particulate material.
Material feeders are used to provide a continuous flow of material into a process at a constant, predetermined feed rate. Gravimetric feeders discharge material into a process on a weigh/time basis, thereby automatically taking changes in the bulk density of the material into account. One class of gravimetric feeders are continuous flow, set rate feeders wherein material is discharged into a process in a continuous stream at a predetermined rate. Belt type feeders are one type of continuous flow, set rate feeders which can be equipped with an accurate weigh/totalizer feature
U.S. Pat. No 3,786,961 to Wahl et al, which is hereby incorporated by reference, discloses a belt type, continuous flow, set rate feeder. The Wahl et al feeder includes a hopper having a spout which discharges material onto a horizontal, endless belt which is mounted between spaced pulleys. A variable speed motor drives one of the pulleys. The horizontal endless belt is pivotably supported at one end by a pair of leaf springs, the belt pivoting downwardly about a horizontal axis in response to the weight of the material on the belt. A load cell arranged beneath the belt at the opposite end of the belt senses the pivotal displacement of the belt, which displacement corresponds to the weight of the material on the belt. The load cell provides an output signal corresponding to the pivotal displacement of the belt to circuitry which regulates the speed of the motor in order to adjust the belt speed in accordance with the deviation of the material discharge rate from a pre-set rate.
Although the Wahl et al belt feeder disclosed in U.S. Pat. No. 3,786,961 works well with most particulate materials, this belt feeder, like all known conventional continuous flow, set rate belt feeders, may not work well with very fine, fluid-like or floodable particulate materials such as fly ash or pulverized coal. This is due to the fact that a flat belt is incapable of holding back a flood of material. That is, a flat belt is incapable of containing very fine particulate materials which tend to behave like a fluid and flow along the belt. Thus, using a flat belt to feed fluid-like or floodable particulate material at a steady, pre-set rate becomes very difficult if not impossible. One means for overcoming the difficulties associated with the belt feeding of fluid-like particulate material is to employ a screw prefeeder which accepts the material from a storage bin and deposits the material onto a weigh belt for weighing and totalizing. The screw flights of the screw prefeeder regulate the flow of material by holding back the flow of material. But of course, the addition of a screw prefeeder increases the cost of the material feeder system.
Other patents which disclose belt feeders include U.S. Pat. No. 3,834,474 to Knol, U.S. Pat. No. 3,884,313 to Engels, and U.S Pat. No. 3,979,055 to Fathauer et al. U.S. Pat. No. 3,834,474 to Knol discloses a metering and conveying apparatus which includes an endless belt having a plurality of spaced, transversely mounted scraper flights on the belt. As material is deposited onto the belt, the belt and the scraper flights apply a force to the material in the conveying direction in order to accelerate the material up to the speed of the conveyor belt. An equal and opposite reaction force is inherently applied to the conveyor by the material as the material is deposited onto the conveyor. This reaction force, which is proportional to the mass of the material deposited onto the belt, is sensed and is correlated with the speed of the conveyor belt by electronic processing apparatus to provide a quantity measurement. The Knol device is not capable of adequately feeding fluid-like particulate material at a pre-set rate despite the existence of the transversely mounted scraper flights on the belt, because the scraper flights are incapable of containing fluid-like particulate material. That is, fluid-like particulate material can readily flow over and around the scraper flights on the belt.
U.S. Pat. No. 3,884,313 to Engels discloses a feeding and measuring device for flowable solid materials. One embodiment of the Engels device includes a chain belt having a plurality of spaced, transversely mounted scrapers on the chains adapted to move the material along a partition and then along the bottom of a housing containing the device. While the scrapers of the Engels device are adequate for their intended purpose of moving or pushing material, they are incapable of containing fluid-like particulate material since such material can readily flow over and around the scrapers. Thus, the Engels device is inadequate to the task of feeding fluid-like particulate material at a continuous, pre-set rate.
U.S. Pat. No. 3,979,055 to Fathauer et al discloses a weighing conveyor system. The Fathauer et al conveyor system includes an upwardly inclined endless chain which is arranged between two parallel sidewalls of a framework. The endless chain includes spaced flights mounted transversely to the chain which flights, apparently, have the function of moving or pushing material up the incline and preventing backward slippage. The in-feed end of the framework is pivotably mounted while the opposite end of the framework is supported by an electronic load cell which senses the weight of the material on the conveyor system. The output of the load cell is combined with a speed related signal produced by a speed sensing assembly to form a combined rate output signal which is further processed to provide a record of a total weight of material signal and a rate weight signal. While the flights mounted on the inclined, endless chain of the Fathauer et al device are capable of pushing material up an incline, the flights are incapable of containing fluid-like particulate material because such material can readily flow over the flights and presumably flow around the flights through the spaces between the flights and the sidewalls of the framework. Thus, the Fathauer et al device is also not adequate to the task of conveying fluid-like particulate material at a continuous, pre-set rate.
While the prior art does disclose various types of belt feeders for conveying or feeding particulate material, the prior art does not disclose a belt feeder which is capable of conveying or feeding fluid-like particulate material at a continuous, pre-set rate, as is the case with the present invention.